1. Technical Field of the Invention
The present invention is related to improving the channel quality in a packet mobile radio network and, in particular, to a method and system therefor using a power control algorithm.
2. History of the Related Art
Power control has traditionally been used in mobile radio networks as a way to improve the channel quality between a mobile terminal and the network. For example, the transmitted power can be increased to improve the carrier-to-interference ratio (C/I) of a channel, thereby improving the data rate or throughput of the channel. The transmitted power can also be decreased to reduce the interference that the channel has on other channels.
An example of such power control can be found in circuit-switched mobile radio networks such as the Global System for Mobile communications (GSM), where the transmitted power is adjusted on an individual channel basis. See, e.g., U.S. Pat. No. 5,574,982 and “Power Control in a Cellular System” by Magnus Almgren, Hakan Andersson, and Kenneth Wallstedt. The adjustments may be made according to any number of known radio link quality measurements such as the received signal strength indicator (RSSI), the C/I, the bit error rate (BER), the bit error probability (BEP), the energy per bit over noise (Eb/No), and the frame erasure rate (FER).
Power control for packet-switched mobile radio networks may be found in a GSM standard, namely GSM 05.08 (version 8.5.0) which includes a proposition for power control in the Enhanced General Packet Radio System (EGPRS).
Similarly, control of the transmitted power is a central function of systems that use code division multiple access (CDMA), as all channels have to share the same set of frequencies. See, e.g., Universal Mobile Telecommunication System (UTMS) standard 3GPP TS 25.214 (version 3.5.0) that provides the power control specifications for UTMS, which is a CDMA system.
In general, however, it is difficult in presently available mobile radio networks to measure radio link quality with a sufficiently high degree of accuracy. Such difficulty arises, in part, because the quality measurements have to be made remotely by the mobile terminals, then transmitted or otherwise reported to the mobile radio networks for processing, thus opening the possibility for reporting errors to occur. The measurement difficulties increase for packet data transmission with short packages and long packet inter-arrival times. This is due to the fact that during non-transfer times, either the measurement accuracy will be lower or the measurement signaling overhead will be larger.
Moreover, radio link quality as reflected by a quality measurement such as the C/I may not be a very good measure of channel quality for mobile radio networks that use packet data. For example, the C/I may not be able to accurately reflect packet delays caused by queuing that decrease the channel data rate and thereby degrade the channel quality. Computer simulations of such packet data mobile radio networks have shown, for example, that users with the worst channel quality do not have significantly lower radio link quality.
Therefore, it is desirable to be able to improve the channel quality in packet data mobile radio networks, and to be able to do so using measurements that more accurately reflect the actual channel quality in such packet data networks.